The instant invention relates to ceramic bodies based on aluminum titanate having low thermal expansion, high porosity, and high strength for use in high temperature applications.
Cordierite ceramic bodies, especially such formed as honeycomb multicellular structures, find employment in a number of high temperature applications such as catalytic converters, NOx adsorbers, electrically heated catalysts, molten metal filters, regenerator cores, chemical process substrates, catalysts for hydrodesulfurization, hydrocracking, or hydrotreating, and filters such as diesel particular filters.
In diesel exhaust filtration, cordierite, being a low-cost material, in combination with offering low CTE, has been the material of choice. Porous cordierite ceramic filters of the wall-flow type have been utilized for the removal of particles in the exhaust stream from some diesel engines since the early 1980s. A diesel particulate filter (DPF) ideally combines low CTE (for thermal shock resistance), low pressure drop (for engine efficiency), high filtration efficiency (for removal of most particles from the exhaust stream), high strength (to survive handling, canning, and vibration in use), and low cost. Problems with cordierite include low volumetric heat capacity and low thermal conductivity which can result in unacceptably high temperatures during operation when the filters are regenerated under certain conditions, as well as low thermal durability. Further, inorganic particulates, known as ash, present in the diesel exhaust can react with cordierite and cause filter failures.
An alternative material to cordierite for DPF manufacturing is SiC. Although this material exhibits both high volumetric heat capacity and high thermal conductivity, it also has poor thermal shock resistance as a result of relatively high thermal expansion and high elastic modulus. The poor thermal shock resistance requires SiC filters to be segmented to prevent thermal shock failure during use. Also, processing requirements (i.e., high temperatures, inert atmospheres, and segmentation) result in high manufacturing costs.
There is a need to provide alternative low CTE materials that are useful in high temperature applications, such as automotive emissions control systems. It would be desirable to provide materials that have a low CTE and excellent thermal shock resistance. The present invention provides such a ceramic material, and a method of making and using the same.